WOAH, THE CURRENT WEEK, WEEK 14 AHHHH

THE HIGHEST FLYYYYY

What does developmental biology study?

How organisms grow and develop from a zygote to an adult, including cell differentiation and pattern formation.

What is morphology in developmental biology?

The study of an organism’s shape and body structure.

Define a zygote.

A single-cell formed by fertilization that gives rise to a multicellular organism through development.

Name four common model organisms used in developmental genetics.

1. C. elegans (worm)

2. Arabidopsis (plant)

3. Zebrafish (D. rerio)

4. Fruit fly (Drosophila)

What are beneficial features of model organisms?

• Short life cycles

• Transparent embryos

• Many offspring

• Easy to manipulate genetically

• Relevant to human biology

What is a common disadvantage of some model organisms?

Some may be less relevant to human development or have limited gene homology.

What is pattern formation?

The process by which cells are spatially organized into tissues and organs during development.

What are the main body axes in animals?

• Anterior-posterior (head to tail)

• Dorsal-ventral (back to belly)

• Left-right

What axis is unique to plants?

The root-shoot axis, which determines the direction of growth and organ formation.

What is radial growth?

Growth outward from a central point, common in plant and some animal structures.

What provides cells with spatial information during pattern formation?

Positional information from morphogens and signaling gradients.

What controls the stages of embryonic development?

A hierarchy of transcription factors regulating differential gene expression.

What do phase 1 transcription factors do?

Set up body axes like anterior-posterior and dorsal-ventral.

What do phase 2 transcription factors do?

Establish body segments.

What do phase 3 and 4 transcription factors determine?

• Phase 3: Organ and limb development

• Phase 4: Cell type identity (e.g., neurons, muscle)

What is a stem cell?

A cell that can self-renew and differentiate into one or more specialized cell types.

What are the two daughter cells from a stem cell division?

One stem cell and one differentiated or differentiating cell.

What does totipotent mean?

Can become any cell type, including embryonic and extraembryonic tissues

What does pluripotent mean?

Can become any cell in the embryo, but not extraembryonic tissues.

What does multipotent mean?

Can differentiate into a limited range of cell types (e.g., adult stem cells).

Where do embryonic stem cells come from?

The inner cell mass of a blastocyst-stage embryo.

What are the advantages of embryonic stem cells?

• Pluripotent

• Can be cultured in vitro

• Have therapeutic potential

What are limitations or concerns with embryonic stem cells?

• Ethical concerns about embryo use

• Risk of tumor formation

What are key features of adult stem cells?

• Found in adult tissues

• Multipotent

• Difficult to isolate

• Involved in tissue repair and maintenance

Name a process in which adult stem cells are involved.

Neurogenesis in the mammalian brain.

What are homeotic genes (Hox genes)?

Genes that control the identity and development of body segments and structures along the anterior-posterior (A-P) axis.

What kind of proteins do homeotic genes encode?

Transcription factors with a homeobox domain that binds DNA.

What happens when a homeotic gene is mutated?

Entire body structures may form in the wrong place (e.g., legs where antennae should be in fruit flies).

How are Hox genes arranged and expressed?

• Arranged in clusters on chromosomes

• Expressed in order from head to tail (A-P axis)

• Often show overlapping expression

What does the homeobox region do?

Encodes the DNA-binding domain of the transcription factor.

What are segmentation genes?

Genes that divide the embryo into segments early in development (e.g., head, thorax, abdomen in Drosophila).

What is the role of Hox genes after segmentation?

They determine the specific identity (e.g., wings, legs) of each segment.

How did scientists discover Hox genes?

By studying mutant flies with abnormal body part placements (e.g., Antennapedia, Bithorax mutants).

What is the Antennapedia mutation?

A gain-of-function mutation causing legs to grow where antennae should be.

What is the Bithorax mutation?

A mutation causing a second set of wings to grow in fruit flies.

Are Hox genes unique to fruit flies?

No — Hox genes are conserved across almost all animals (except sponges).

What does the conservation of Hox genes across animals suggest?

That they were present in a common ancestor, and developmental mechanisms are evolutionarily conserved.

How many Hox gene clusters do vertebrates have?

Four clusters on four different chromosomes.

What axis do Hox genes help pattern in animals?

The anterior-posterior (A-P) axis.

Hox genes encode membrane-bound proteins.

❌ False — they encode transcription factors.

Hox gene mutations can lead to body parts developing in incorrect locations

✅ True

Homologous Hox genes exist in all animals.

❌ False — they are not found in sponges.